Flame retardant epoxy resin composites modified with organophosphorus and boron hybrid molecules

doi:10.11949/0438-1157.20201832

Abstract

Abstract:

As a common polymer material, epoxy resin (EP) is flammable. Traditional EP usually loses its transparency after flame retardant incorporated. Besides, it is hard to obtain the satisfying flame-retardant efficiency with low loading amount. In this work, two kinds of flame retardant with organophosphorus/boron hybrid were successfully synthesized (abbreviated as: DPC-1B and PDS-2B) by simple reaction between diphenylphosphinyl chloride/phenylphosphoryl dichloride and 4-hydroxyphenylboric acid. After introduced 2.0%(mass) of DPC- 1B or PDS-2B, the EP composite reached V-0 rating in the UL-94 vertical burning test and the limited oxygen index (LOI) values increased from 25.7% to 31.8% and 31.5% respectively. Interestingly, the EP composite still presented excellent transparency. Furthermore, the peak heat release rate of the flame retardant EP decreased 26.5% and 21.8%. Due to the combination of boron and phosphorus, a dense carbon layer was formed, which insulated the heat and achieves the flame retardant effect. Accordingly, the two novel flame retardant demonstrate promising applications in the flame retardant of EP without sacrifice of transparency.

Key words: organic compounds, polymers, flame retardant, mechanical properties, transparency

摘要：

从二苯基次膦酰氯和苯基磷酰二氯出发，分别合成了含单个苯硼酸基团和含两个苯硼酸基团的两种有机磷/硼杂化小分子（缩写为：DPC-1B和PDS-2B）。两种杂化小分子与环氧树脂有着良好的相容性并可参与环氧固化，在比较低的添加量下便有较高的机械强度和优异的阻燃性能，且保持环氧的透明度。DPC-1B和PDS-2B添加量为2%（质量）时，复合材料氧指数从25.7%分别提高到了31.8%和31.5%，热释放速率峰值分别降低了26.5%与21.8%，UL-94阻燃等级均达到了V-0级。改性环氧树脂燃烧后的残炭分析表明，炭层外部连续紧密，内部多蓬松，硼磷共同作用形成致密炭层，隔绝热质传递，从而达到阻燃效果。

关键词: 有机化合物, 聚合物, 阻燃, 力学性能, 透明度

CLC Number:

TQ 314.22

JI Rongbin, CHEN Ting, PENG Chaohua, XIA Long, CHEN Guorong, LUO Wei'ang, ZENG Birong, XU Yiting, YUAN Conghui, DAI Lizong. Flame retardant epoxy resin composites modified with organophosphorus and boron hybrid molecules[J]. CIESC Journal, 2021, 72(7): 3856-3868.

纪荣彬, 陈婷, 彭超华, 夏龙, 陈国荣, 罗伟昂, 曾碧榕, 许一婷, 袁丛辉, 戴李宗. 有机磷/硼杂化小分子阻燃改性环氧树脂[J]. 化工学报, 2021, 72(7): 3856-3868.

Figures/Tables 19

Fig.1 Synthetic route of DPC-1B

Fig.2 Synthetic route of PDS-2B

Fig.3 1H (a), 31P (b) and 13C (c) NMR spectra of DPC-1B

Fig.4 1H (a), 31P (b) and 13C (c) NMR spectra of PDS-2B

Fig.5 FT-IR spectra of DPC-1B and PDS-2B

Table 1 Thermal decomposition data of DPC-1B and PDS-2B

Samples	Nitrogen					Air
Samples	T_o/℃	T_max1/℃	T_max2/℃	T_max3/℃	W_re/%	T_o/℃	T_max1/℃	T_max2/℃	T_max3/℃	W_re/%
DPC-1B	120.80	134.40	288.31	432.73	11.53	116.75	143.36	290.43	400.11	19.62
PDS-2B	100.12	113.21	392.53	515.16	36.55	93.29	122.25	398.43	518.77	31.13

Fig.6 TG (a), (c) and DTG (b), (d) curves of DPC-1B and PDS-2B under nitrogen atmosphere and air atmosphere

Fig.7 TGA (a) and DTG (b) curves of cured epoxy resin

Table 2 TGA data of cured epoxy resin

Samples	Nitrogen
Samples	T_o/℃	T_max/℃	W_re/%
EP	355.3	392.65	12.66
EP/1% DPC-1B	352.4	387.89	15.28
EP/2% DPC-1B	347.0	390.84	16.12
EP/1% PDS-2B	343.6	388.95	16.66
EP/2% PDS-2B	340.9	389.88	19.27

Table 3 LOI and UL-94 vertical burning data of cured epoxy resin

Samples	LOI/%	UL-94
Samples	LOI/%	T₁/s	T₂/s	Dripping	Rating
EP	25.7	>30	—	Yes	NR
EP/2% DDP	28.9	17	11	No	V-1
EP/2% HPB	26.6	25	14	No	V-1
EP/2% PB	30.1	12	6	No	V-1
EP/1% DPC-1B	31.1	6	1	No	V-0
EP/2% DPC-1B	31.8	3	1	No	V-0
EP/1% PDS-2B	31.0	11	3	No	V-1
EP/2% PDS-2B	31.5	3	3	No	V-0

Fig.8 HRR (a), THR (b), SPR (c) and TSP (d) curves of EP, EP/1% DPC-1B, EP/2% DPC-1B, EP/1% PDS-2B and EP/2% PDS-2B

Table 4 Cone calorimeter tests data of cured epoxy resin

Samples	TTI /s	PHRR/(kW/m²)	THR/(MJ/m²)	FIGRA/(kW/(m²·s))	SPR/(m²/s)	TSP/m²	Residue/%(mass)
EP	101	1042.5	128.5	5.75	0.16	20.7	10.3
EP/1% DPC-1B	99	908.3	117.4	4.88	0.17	22.4	17.0
EP/2% DPC-1B	101	766.5	103.7	4.16	0.20	21.5	24.2
EP/1% PDS-2B	100	958.7	110.8	5.26	0.16	19.6	20.0
EP/2% PDS-2B	99	815.1	106.7	4.40	0.16	19.2	23.6

Fig.9 Optical images of char residue after cone calorimeter tests

Fig.10 SEM images of char residue internal and exterior obtained from cone calorimeter tests for EP, EP/1% DPC-1B, EP/2% DPC-1B, EP/1% PDS-2B and EP/2% PDS-2B

Fig.11 FT-IR spectra of EP, EP/2% DPC-1B and EP/2% PDS-2B char

Fig.12 Changes of DPC-1B and PDS-2B after heating

Fig.13 The optical photographs (a) and UV-Vis spectra(b) of cured epoxy resin; Curing curves of EP cured tested by DSC (c)

Fig.14 DMA (a) and tanδ (b) curves of cured epoxy resin

Table 5 Three-point bending test data of cured epoxy resin

Samples	Flexural strength/MPa	Elasticity modulus/(N/mm²)
EP	87.39	2045.9
EP/1% DPC-1B	98.13	2230.1
EP/2% DPC-1B	103.45	2328.4
EP/1% PDS-2B	114.80	2357.5
EP/2% PDS-2B	126.34	2391.3

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